Inductively coupled passive responder and interrogator unit having multidimension electromagnetic field capabilities

ABSTRACT

An interrogator-responder system wherein the responder is a passive responder receiving an inductively coupled electromagnetic power field from an interrogator unit and generating an unique predetermined electromagnetic coded information field in response to the presence of the electromagnetic power field. The interrogator unit has multidimensional recognition capabilities for detecting the electromagnetic coded information field independent of the orientation of the responder for two dimensional or three dimensional capabilities.

United States Patent [1 1 3,689,885

Kaplan et al. Sept. 5, 1972 [54] INDUCTIVELY COUPLED PASSIVE 3,088,1064/1 963 Smith ..343/6.5 RESPONDER AND INTERROGATOR 3,384,892 5/1968Postman ..343/6.5 UNIT HAVING MULTIDIMENSION ELECTROMAGNETIC FIELD 'yExaminer-Donald Yusko CAPABILITIES AttorneyFinkelstein & Mueth [72]Inventors: Leon M. Kaplan; Thomas A. Kriof [57] ABSTRACT sky, both ofGoleta, Calif. A d h h n mterro ator-res n er s stem w erem t e [73]Asslgneez Trans'tag Corpomnon responder is a passiv responde r receivingan induc- [22] Filed; Sept. 15, 1970 tively coupled electromagneticpower field from an in-' terro ator unit and eneratin an uni ue redeter-[211 App! 72483 minet i electromagnet ic coded informz tion field in 4response to the presence of the electromagnetic power [52] US. Cl..340/152 T, 325/15, 343/68 fi ld- Th nterr gator unit has multidimnsional [51] Int. Cl. ..H04q 7/00 recognition capabilities for detectingthe electromag- [58] Field of Search ..340/149, 152; 325/8, 15, 51;netic coded information field independent of the 343/65, 6.8 orientationof the responder for two dimensional or three dimensional capabilities.

[56] References Cited 40C 11 D v launs, rawmg Figures UNITED STATESPATENTS 3,018,475 1/1962 Kleist etal ..343/6.5

\o lNTERROGATOR I RESPONDER TAG P- 22 I 1 {i 1 POWER ELECTRO I suppPOWER MAGNETIC 'VVU P x SlNAL POWER TIME GEN FlELD EM R D Ems-E GENPOWER C EN FlELf? ll I i (FREQI- l) f I I 2a ,2.

I INFORMATION E M CLARRlER EM ODE CAPTURE INEORMMZON CODED 'HMF. coma$55,33 CODED 8mm, ew 1 52:: L 1

LOGIC. DETEUOR RECEIVER GEN 6%? l 58 1 26 l 4o rm I FEW NFORMATON E mCODED lNF-ORMAHON WW ig fii 5) (FREQ F2) on COMMU- N\CAT\ON PATENTEUSEP5 I972 sum 8 or 8 booooooooooo N VN Toes 150 M, KAPLAA/ 7740/1445 4.kR/OA K y BY INDUCTIVELY COUPLED PASSIVE RESPONDER AND INTERROGATOR UNITHAVING MULTIDIMENSION ELECTROMAGNETIC FIELD CAPABILITIES BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to theidentification art and more particularly to an improvedinterrogator-passive responder arrangement for providing an uniqueidentification of a moving or stationary object in response to aninductively coupled signal from the interrogator.

2. Description of the Prior Art A number of systems have been proposedin the past, and some have been utilized, for remote detection of anunique identification code on a responder that is placed upon a movingobject. In such application the code detection generally comprises aninterrogator means that is positioned in signal exchange relationship tothe responder. One application of such a system is, the identificationof individual cars of a freight train, individual buses on city streets,or the like. In such applications, though, there is generally provided afixed and known relationship between the coded identification on themoving objector there is generally a predetermined motion of the movingobject at a known speed in a fixed direction. Thus, these systems havegenerally comprised single dimension identification arrangements in thatthe interrogator was oriented to detect the data in a fixed path as themoving object passed the interrogator. Since the movement of freightcars, buses or the like are generally in a single dimension with respectto the interrogator, there is no requirement to provide multidimensiondetection capability.

Most interrogator-responder identification systems known heretofore aredesigned such that the interrogation and the response are either both inthe form of radiated high frequency energy or such that theinterrogation is in the form of low frequency (non-radiated) energy andthat the response is in the form of high frequency radiated energy.Disadvantages to such systems include:

1. generation of rf interference in the environment;

2. complexity due to the requirement to maintain the output frequencywithin an assigned portion of the radio-frequency spectrum;

3. physical length of the responder radiating element is relativelylarge thereby limiting the minimum size of the responder. Theidentification system described herein operates in an entirelynon-radiating mode thereby avoiding radio frequency interferenceproblems.

Methods in the prior art used for generating specific codecharacteristics have usually involved frequency coding wherein thebinary value of the code is established by the occurrence ornon-occurrence of specified frequencies. For example, modulation of acarrier is accomplished by means of selected lower frequency signals,selected higher harmonic frequencies of the carrier or selectivesuppression from the carrier of predetermined frequencies.

Aside from radio frequency interference considerations, disadvantages tosuch systems include:

1. responder complexity due to the requirement for a relatively largenumber of tuned circuits or filter elements to achieve a large number ofunique identification codes;

2. interrogator complexity due the requirement to generate andselectively sense a large number of frequencies;

3. responder tuned circuit bandwidth control problems if inductors areused in the tuning circuit due to detuning in the presence offerromagnetic background materials.

In several cases of the prior art methods are suggested for generatingunique time code sequences but as far as is known such patents have notshown how the required energy for the logic and switching circuitry isderived except by means of a responder battery. Time coding offersadvantages over frequency coding in that a very large number of uniquecodes may be obtained with less complexity than with a frequency codedsystem. That is, as the number of required information bits becomeslarger the time code approach becomes increasingly advantageous.

In certain prior art devices, there was utilized the fundamentaltechnique of modulating the interrogator frequency by varying theimpedance in a responder tuned circuit which is inductively coupled tothe interrogator signal source.

In the system described herein, the responder uses the energy in thefield provided by the interrogator to both generate a new non-radiatedcarrier and to time code modulate this carrier. Furthermore, in oneembodiment of the system described herein the periodicity of theinterrogator field is used to establish the code information rate.

Certain prior art devices also require the ideal" orientation of theinterrogator source field with the responder coil element, and do notoperate in other orientations.

There are other interrogator-responder systems in the prior art, such assome shown in Twenty-one Ways to Pick Data Off Moving Objects," RobertJ. Barber, Control Engineering, Oct. 1965 and Jan. 1964, that useinductive or transformer coupling to derive power for the respondercircuitry. However, as far as is known, only the ideal one dimensionalcase has been considered, i.e., these devices show a preferredrelationship necessary for successful operation between the interrogatorpower output coil and responder pickup coil such that these coils areoriented with the coil axes parallel to one another. In such cases,often the responder uses the power to modulate a radio frequencycarrier, i.e., it is a radiating system.

It will be appreciated that in certain applications requiring thedetection of an unique coded signal associated with a moving object, theapparatus for generating the coded signal must be comparativelyinexpensive, preferably passive to minimize cost, weight and size, andrequire comparatively low power for operation to minimize thetransmitted power between the interrogator and the responder. Where verylarge scale mass production is anticipated, the responder must, ofcourse, be capable of being mass produced at low cost, have a largenumber or code identification capacity. I

There are those applications in which the orientation of the responderwith respect to the interrogator will be completely random and will varyfrom responder to responder thus, three dimensional detection capabilitymust be provided. Further, other applications often require at least twodimensional detection capability. That is, while the responder may havea known orientation in one dimension with respect to the interrogator,it may be unknown in orientation in the other two dimensions.

For example, in many industrial plants it is often desirable to know theprecise location of guards, watchmen, executives or the like.Accordingly, a small inexpensive non-radiative passive responder couldbe carried by such people and each responder would be precoded togenerate a known unique identification signal in response to thecoupling of power into the responder. interrogators could be positionedat various locations throughout the plant for continuously generatingpower fields for inductive coupling into the responder. As the personnelcarrying the responder tags pass successive interrogators, theirdetected signals would be recorded and an appropriate visual displayand/or computer entry could be made to show the precise location of theperson. In such arrangements, of course, the responder tag may be in anyorientation with respect to a given interrogator at the time the personpasses by the interrogator.

Another application in which orientation of the responder with respectto the interrogator will be completely random is in the handling ofluggage and cargo in airport terminals, freight terminals or the like.In this application, the entire system comprising the loading andunloading of the luggage must be considered and the identification of aparticular piece of luggage forms an integral part of such a system. Itwill be appreciated that for such a system three dimensional readingcapability is preferred and the responder tags which may be placed uponthe luggage or cargo should be comparatively inexpensive, passive,non-radiative and have a sufficient code capacity for any desired numberof information bits.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of theinvention herein to provide an improved interrogator-responderarrangement for detecting an unique coded signal on a moving orstationary structure.

It is another object of the invention herein to provide an improvedpassive responder tag for generating an unique coded signal in responseto an inductively coupled power signal applied thereto.

It is yet another object of applicants invention herein to provide animproved interrogator for generating a power field within inductivecoupling range of an appropriate passive responder and for receiving anunique coded identification field in response thereto and providing anoutput signal having an information content corresponding to the uniquecoded signal in the responder.

It is another objective of this invention to provide aninterrogator-responder identification system wherein the responderderives all of the energy to power its timing, logic, coding and outputcircuitry from the interrogator.

It is a further object of this invention to provide aninterrogator-responder identification system arrangement in which thecapability exists to couple power and reliably transfer the respondercode to the interrogator without regard to the phase inversion or theorientation of the power field receiving and coded information fieldgenerating coils of the responder with respect to the power fieldgenerating and coded information field receiving coils of theinterrogator.

It is a further object of this invention to provide aninterrogator-responder identification system in which the identificationcode of the responder is established by modulating a low frequencynon-radiating carrier generated on the responder.

It is a further object of this invention to provide aninterrogator-responder identification system in which the timeinformation (periodicity) of the interrogator carrier is used toestablish the modulation pulse rate on the responder carrier therebyavoiding the requirement for a separate time base generator on theresponder for this purpose.

It is a further object of this invention to provide aninterrogator-responder identification system in which the means ofmodulating the responder carrier provides the capability to reliablyrecognize each information bit time for the purpose of clocking thedemodulated responder coded information signal in the interrogator,thereby avoiding ambiguity in the code recognition due the unknownorientation of the responder with respect to the interrogator.

It is a further object of this invention to provide aninterrogator-responder identification system with a responder capabilityfor generating a very large number of unique code combinations in asmall size and form amenable to mass production.

As noted above, there are many applications wherein it is desired tohave a full three dimensional detection capability between the responderand the interrogator. According to the principals of the inventionherein, the invention is described as utilized in an automatic luggagehandling system incorporating, as part of the system, the improvedinterrogator and responder according to the principals hereof.

However, for a better understanding of the operation of the inventionthe following description of an overall automatic luggage handlingsystem incorporating the improved interrogator-responder arrangement ofthis invention is provided. In such an automatic luggage handling systema responder tag, having certain characteristics as described below, isattached to each individual piece of luggage at the check-in station orat the ticket collection station such as at an airport terminal. Thistag may be affixed in any desired manner on the luggage and may, forconvenience, be just generally attached to a handle to eliminate thenecessity for a predetermined orientation. Since each tag has a uniquecode generation capability, the presence of the responder tag on thepiece of luggage provides the capability for automatically identifyingthe luggage at any point along the route. The code on the tag may, ifdesired, indicate any desired information bit concerning the passenger,the flight, the ultimate destination, the routing, the number of piecesof luggage for this passenger, or the like. This is merely a designselection criteria. Alternatively, while each tag may have an uniquecode generating capability, the tags may be completely reusable and theparticular code on each tag would then correspond to the recordedinformation on the passenger as indicated above. That is, the tag wouldnot be changed for each passenger but merely the information associatedwith a passenger would correspond to a particular tag code. In oneproposed arrangement for utilizing an automatic luggage handling systemincorporating the improved interrogator tag, at the time of placing thetag on the luggage a second responder tag having a code generationcapability that provides either the same code as the one affixed to theluggage or bears a known correspondence to the one attached to theluggage is given to the passenger. (For example, odd numbered tags maybe utilized on the luggage and the next highest even number for each taggiven to the passenger.)

The luggage is carried then in the conventional.

manner and upon arrival at its destination the passenger obtains hisindividual piece of luggage'by utilizing the responder tag in hispossession. Inserting that into the baggage request station automatichandling equipment is provided to detect the particular code on the tag,find the particular piece of luggage having the code thereoncorresponding to the passengers tag and moving that piece of luggage tothe awaiting passenger. On receipt of the luggage the passenger may thenbe allowed to remove the luggage from the area by placing both tags intoa return comparator slot and, if the correct correspondence between tagsis present, the gate opens allowing the passenger to leave and the tagsare retained, stacked and returned to, for example, the airline forre-utilization.

It will be appreciated that in addition to the interrogator fordetecting the coded signal on the tags, and the responder tags, thereare many other major components of such an automatic baggage handlingsystem. These would comprise, of course, conveyor belts, luggagetransfer units, check-in stations, luggage sorting stations, luggagerequest stations, checkout stations and a digital communication cable.

Any combination of the above-mentioned additional components may beperformed manually, if desired, and still allow utilization for a moreefficient luggage identification and removal by the passenger. Theabove-mentioned systems are merely indicated as functional necessitiesand they may be combined or eliminated as economically practical or aslimited by other factors.

The present invention, of course, is concerned with the interrogator andthe responder tags. In such an application, one embodiment of thepresent invention may incorporate an interrogator means for generatingan electromagnetic power field at frequency fl within inductive couplingrange of the responder tag, and, in turn, receiving the electromagneticcoded information field at frequency f2 generated by the responder tagand then providing an output signal having an information contentcorresponding to the electromagnetic coded information field received.The interrogator may comprise a power supply means for generating acontrolled source of electrical energy and a power signal generatormeans that receives the controlled source of electric energy andgenerates a power signal in response thereto. The power signal generatormeans is coupled to an electromagnetic power field generator which isutilized to provide the electromagnetic power field to be coupled fromthe interrogator to the responder tag. In this application of theinvention the interrogator and responder tag are inductively coupled toeach other for the transmission of the electromagnetic power field fromthe interrogator to the responder tag and for the transmission of theelectromagnetic coded information field from the responder tag back tothe interrogator means.

The interrogator means also has a coded information field receiver meansand, in one embodiment of the invention, the power field generator meansand the coded information field receiver means of the interrogator meanscomprise a plurality of three induction coils arranged in an orthogonalrelationship and may further comprise a switching means for sequentiallyswitching each of the coils from a power generating condition to aninformation signal receiving condition at a predetermined switchingfrequency rate. One embodiment of the invention has one of the coils inthe transmitting condition and two of the coils in the receivingcondition and the coils are sequentially switched in a predeterminedsequence.

The interrogator also is provided with a coded information signaldetection means that detects the coded information signal received bythe coded information field receiver, and a logic means that receivesthe detected coded information signal. The logic means incorporatesstructure for detecting a keying or synchronization portion of the codedinformation signal as well as the unique portion of the informationsignal. The logic means then generates an output signal having aninformation content corresponding to the unique portion of theinformation signal. The output signal may then be utilized in anystorage or display or communications means as desired.

A time-base signal generator means is provided in the interrogator andis applied to both the power signal generator and the logic means forappropriate timebase synchronization.

A responder tag means is preferably a comparatively small tag and may,for example, be on the order of 2X3X/32 inches. In order to minimizecomplexity and allow incorporation of the tag into this small size,wherein it is preferably imbeded, it is preferred that integratedcircuit techniques be utilized in order to minimize such size. Further,in order to minimize the cost in fabricating such tags on a large scalebasis, it is preferred that a monolithic integrated circuit be utilizedto implement as many facets of the responder tag as practical.

The responder tag is provided with an electromagnetic power fieldreceiver means that receives the electromagnetic power field atfrequency fl from the interrogator and provides a DC responder tag powersignal in response thereto. The receiver means on the responder tag may,in this embodiment, comprise a coil with a high permeability core meansto maximize magnetic flux capture and having means for full waverectification and filtering which may comprise a diode bridge. Sinceinductive coupling is provided between the interrogator and theresponder, the signal strength varies with physical separation betweenthe responder and interrogator. Accordingly, a DC voltage magnitudelimiting means, which may be a zener diode, is incorporated in the fieldreceiver means so that the DC power signal does not exceed apredetermined magnitude. The electromagnetic power field receiver meansalso provides, in this embodiment, an AC signal at frequency f which mayprovide a stimulus input to the carrier time-base signal generatingmeans and the code signal generating means to be subsequently described.

The responder also has a carrier time-base signal generating means thatreceives the DC responder tag power signal and generates a carriertime-base signal at frequency f,, to the DC tag power applied to thecarrier time-base signal generator means. It has been found that byhaving the carrier time-base signal at a comparatively high frequencysuch as, for example f =450 kiloHertz, and the electromagnetic powerfield at a lower frequency, for example, f,=50 kiloHertz, interferencebetween the electromagnetic coded information field and theelectromagnetic field is minimized. The carrier time-base signal may begenerated by utilizing a higher harmonic of the electromagnetic powerfield frequency f or by utilizing a self container oscillator operatingat frequency f The responder tag also has a code signal generator thatreceives the DC responder tag power signal and repetively generates anunique code signal. Utilization of metal oxide semiconductors,complimentary metal oxide semiconductors, silicon on sapphiresemiconductor or other semiconductor arrays that provide high densitytransistor and/or diode configurations and require relatively lowoperating power are preferably incorporated as a portion of the codesignal generator. These arrays are, of course, pre-encoded on assemblyso that they repetitively generate the unique code in response to thepresence of the DC responder tag power signal.

The code signal may be generated directly by utilizing the periodicityof the electromagnetic power field at frequency f or harmonics or byutilizing a self-contained oscillator operating at frequency f;,, wheref is significantly less than f and may equal f,

In one embodiment the information content of the code signal ispresented in binary code decimal form. In the binary coded decimal, fourbits represent the binary number. It has been found that one binary bitnotation O] l l 1 l 1, together with one bit for parity identificationdoes not represent a number sequence in this binary coded decimalformat. Therefore, in this format these eight bits can be utilized as asynchronizing or keying portion of the information signal. That is, asthe code signal generator repetitively generates the code a firstportion of the information bits in the codes comprises theabove-mentioned synchronizing or keying portion which may be common toall the responder tags and then the remainder of the binary bits in theinformation code comprise the unique binary code identification numberfor that particular responder tag.

The unique identification code generated by the code signal generator inthis embodiment is applied to a coded information signal generator as isthe carrier time-base signal. The coded information signal generatorthen modulates the carrier time-base signal with the code signal toprovide the coded information signal that is coupled into anelectromagnetic coded information field generator means which maycomprise an induction coil from which it is inductively coupled back tothe electromagnetic coded information field receiver of the interrogatormeans. Thus, as long as the power input field is present at the powerfield receiver of the responder tags, there will be a repetitivegeneration of the coded information field for inductive coupling back tothe interrogator.

The logic in the interrogator has appropriate means for detecting thesynchronizing or keying portion of the information signal and providingthe output signal corresponding to the unique information code.

When the responder tag is affixed to an item without respect toorientation, such as a piece of luggage as mentioned above, the itempasses through the three orthogonal coils of the electromagnetic powerfield generator and coded information field receiver in theinterrogator. Thus the interrogator is in a fixed location and the coilsare sufficiently enlarged enough to allow the item to pass through.While the item is within the coils the interrogator is continuouslygenerating the power field within inductive coupling range of theresponder tag and, as noted above, the responder tag is continuouslygenerating the unique coded information field therefrom. Since the threeorthogonal coils are sequentially switched from the signal transmittingto the signal receiving condition, and back, the orientation of theresponder tag with respect to the three orthogonal coils is immaterialand the coded information field will thus be sensed for any threedimensional orientation of the responder tag.

In other embodiments of the invention the power field generator of theinterrogator comprises a pair of compressed interrogator coils that areutilized for generation and projection only and a separate coilorthogonal to the interrogator coils is utilized as the codedinformation field receiver. Such a unit, when the long axes of theinterrogator coils are mutually perpendicular, can provide both twodimensional information signal detection capability as well as a certaindegree of angularly limited three dimensional detection capability.

In yet another embodiment of the invention the power field generatorcomprises a single compressed interrogator coil that is utilized forgeneration and projection only and a separate coil orthogonal to theinterrogator coil is utilized as the coded information field receiver.Such a unit can provide both one dimensional information signaldetection capability as well as a certain degree of angularly limitedtwo and three dimensional detection capability.

In yet another embodiment of the invention the power signal generatorand electromagnetic power field generator of the interrogator and thepower field receiver of the responder may be replaced by an active powersource within or coupled electrically to the responder. Such a unit canprovide a simplification of the identification process such that theforementioned interrogator becomes merely a receiver in applicationswhere a power source is available on the item to be identified, such asa vehicle, or an increased physical size of the responder can betolerated.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other embodiments of theinvention are more fully understood from the following detaileddescription taken together with the accompanying drawings whereinsimilar reference characters refer to similar elements throughout and inwhich:

FIG. 1 is a block diagram of an interrogatorresponder tag systemaccording to the principals of this invention;

FIG. 2 is a circuit diagram, partially in block diagram form, of theresponder tag;

FIG. 3 is a circuit diagram of a squaring amplifier shown in FIG. 2;

FIG. 4 is a circuit diagram of a gated linear amplifier shown in FIG. 2;

FIGS. 5A and 5B show a circuit diagram, partially in block diagram form,of the interrogator without the logic section;

FIG. 6 is a detail configuration of the interrogator electromagneticpower field generator;

FIG. 7 is a block diagram of the interrogator logic section;

FIG. 8 is a timing diagram of the information capture and validationlogic;

FIG. 9 is a pictorial of an interrogator with two dimensionalcapabilities;

FIG. 10 is a section view of the two dimensional interrogator coilarrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 thereis shown, in block diagram form, the general arrangement of oneembodiment generally designated 10 of a preferred form of aninterrogator and responder tag according to the principals of theinvention.

As shown, the interrogator means, generally designated 12, is comprisedof a power supply 14 for generating a controlled source of electricenergy that is utilized to provide the basic power for the interrogatormeans 12. A time-base generator 16 is operatively connected with thepower supply 14 and generates an appropriate time-base signal.

A power signal generator 18 receives the controlled source of electricenergy from the power supply 14 as well as a time-base signal from thetime-base generator 16 and generates an AC power signal that is coupledinto an electromagnetic power field generator means 20 operating atfrequency f,. The power field generator means, in this embodiment of theinvention, may comprise one or more induction coils that is utilized togenerate an electromagnetic power field within inductive coupling rangeof the responder tag generally designated 22. The responder tag 22 hasan electromagnetic power field receiver means 24 which, in a preferredembodiment, may comprise a high permeability coil means for theinductive coupling to extract energy from the power field provided bythe power field generator 20 and the power field receiver 24 generates aDC responder tag power signal in response to the presence of the powerfield applied thereto. The DC responder tag power signal is utilized toprovide the power for the responder tag. In this embodiment of theinvention the responder tag 22 is passive and all power into theresponder tag 22 is from the electromagnetic power field inductivelycoupled into the power field receiver 24.

The responder tag 22 also comprises a carrier time base signal generator26 operating at frequency f that receives the DC responder tag powersignal and generates an AC carrier time-base signal in response thereto.The AC carrier time-base signal is selected to have a frequencysubstantially different from the electromagietic power field frequency.For example, the electromagnetic power field may have the frequency onthe order of f,=50 kiloI-Iertz and the carrier timebase signal frequencymay be on the order of fg=450 kilol-lertz in order to preventinterference between the electromagnetic power field and theelectromagnetic coded information field coupled to the interrogator 12by the responder tag 22, as described below.

The AC carrier time-base signal generator 26 may comprise a frequencymultiplier utilizing the electromagnetic power field frequency f as theinput frequency and a higher harmonic of f; as the output frequency f ora self contained oscillator operating at frequency f The carriertime-base signal is coupled into the coded information signal generator28 that also receives an unique code signal from a code signal generator39. The code signal generator 30 may be an integrated circuit comprisinga metal oxide semiconductor multiplexer, a complimentary metal oxidesemiconductor multiplexer, silicon on sapphire semiconductor multiplexeror the like. That is, it should provide a high information bitcapability in a comparatively small volume and utilizing a comparativelysmall amount of power. The code signal generator 30 generates a codethat is unique to the particular responder tag and the code signalitself is comprised generally of a binary notation code in which thereis provided a plurality of bits corresponding to each information digit.Eight bits are utilized as a synchronization or keying portion of thecode signal in this embodiment. The remaining bits in the code signaldefine, in binary terms, in this embodiment, an information signalportion that is unique to the particular responder tag.

The code signal generator 30 may comprise a multiplexer control counterwhich utilizes the frequency f of the electromagnetic power field or asub harmonic as the signal frequency or which utilizes the frequency ofa self contained oscillator as the code signal frequency.

The code signal is applied to the coded information signal generator 28from the code signal generator 30 and it is utilized to modulate thecarrier time-base signal. In the embodiment shown in FIGS. 1 and 2 themodulation is am amplitude modulation.

The coded information signal comprising the amplitude modulated carriertime-base signal is inductively coupled from the electromagnetic codedinformation field generator 32 to the electromagnetic coded informationfield receiver 3 of the interrogator means 12. The appropriate signalforms at the various portions of the responder tags are indicated onFIG. 1.

The coded information signal receiver may, as noted above, beincorporated into a plurality of three induction coils in an orthogonalorientation to serve sequentially the functions of both the codedinformation field receiver 34 and the power field generator 20.

The coded information signal is detected in the coded information signaldetection stage 36 and the detected coded information signal is fed tothe logic stage 38. The logic stage detects the synchronizing and keyingportion of the information signal and then generates an output signalhaving an information content that corresponds to the unique informationportion of the information signal after checking for parity and truesignal detection. The output signal may then be utilized in any type ofstorage or display or communication device 40 desired.

FIG. 2 illustrates the responder tag 22 shown in FIG. 1. As shown inFIG. 2 the power field receiver 24 that receives the electromagneticpower field is, in this embodiment of the invention, comprised of aplurality of three loop-stick coils 42, 44 and 46 for providing theinductive coupling to the AC power input signal and three four diodebridge means 48, 50 and 52 utilized as full wave rectifiers. The numberof such bridge means and the number of different DC voltages that mustbe provided depends upon the particular circuit parameters and types ofcomponents utilized in the responder tag 22. As shown, diode bridge 48and coil 42 provide a +6 volt signal, diode bridge 50 and coil 44provide a 6 DC signal and diode bridge 52 and coil 46 provide a 28 voltDC signal. Since the magnitude of the DC voltages that are generated inthe diode bridges 48, 50 and 52, are proportional to the proximity ofthe responder tag 22 to the power field generator of the interrogatormeans 12, zener diodes 54, 56 and 58 are incorporated as DC voltageamplitude limiting means so that overly high DC voltages are notgenerated in the responder tag 22 if the responder tag 22 happens to beexceptionally close to the interrogator means 13. Similarly, filtercapacitors, 55, 57 and 59 are incorporated to eliminate ripple.

The carrier time-base signal generator 26 is comprised, in thisembodiment of the invention, of a squaring amplifier 60 that receivesboth the DC responder tag power signal at 28 volts from diode bridge 52as well as an AC signal tapped between the coil 46 and the diode bridge52 at the electromagnetic power field frequency f which, as noted above,may be on the order of 50 kiloHertz. The squaring amplifier 60 providesessentially a squarewave at frequency f that is fed into a filter means62. The filter means 62 may, in this particular embodiment of theinvention, comprise a Clevite Model 202A ceramic filter and the filtermeans 62 converts the squarewave signal at frequency into the carriertime-base signal at frequency f for example, 450 kiloI-Iertz. Thecarrier time-base signal at frequencyf, is fed into a gated linearamplifier 64 which, in this embodiment of the invention, provides theappropriate modulation of the carrier time-base signal as describedbelow. The gated linear amplifier 64 also receives the +6 volt signalfrom the diode bridge 48 and the 6 volt signal from the diode bridge 50,in accordance with well-known electronic practice techniques. It will beappreciated by those skilled in the art that changing the particularcomponents in the responder tag 22 can change the requirements for aparticular voltage level. Therefore this invention is intended to coverall such variations of the responder tag that comprise variations ofcomponents necessitating different voltage signals.

The code signal generator 30 utilizes and may be considered toincorporate as part of it the squaring amplifier 60 as well as thecounter/multiplexer stage 66. The counter/multiplexer stage 66 may beany desired type of counter/multiplexer, such as a Philco-Ford PL 4516and generally comprises a counter-stage 68, a plurality of AND gates 70,and a plurality of OR gates 72. The counter 68 receives the DC respondertag power signal from the diode bridge 52 as well as the squarewave fromthe squaring amplifier 60 at frequency f When the multiplexer 66 is, forexample, metal oxide semiconductor type multiplexer such as thePhilco-Ford Model PL 4516, the sequencing through the counter, AND gatesand OR gates proceeds in accordance with the known design parametersthereof and the switch means 74 indicated as coupled to the AND gates isrepresentative of a grounding switch for each individual AND gate. Thus,depending upon the particular binary code number that is encoded intothe counter/multiplexer 66 before it is incorporated into the respondertag 22 the counter/multiplexer 66 generates an output signal comprisinga code signal that is fed into the gated linear amplifier 64 forappropriate modulation of the carrier time-base signal.

In the preferred embodiments of the invention, the coded informationsignal comprises a binary signal and as shown by the embodimentillustrated in FIG. 1 and in FIG. 2 the coded binary signal is appliedas an amplitude modulator to the carrier time-base signal in the gatedlinear amplifier 64 which feeds the modulated signal into theelectromagnetic coded information field generator 32 which comprises aresponder coil 76. Capacitor 77 may be included for the coil 76. Theresponder coil 76 is an induction coil and inductively couples theindicated amplitude modulated field back to the coded information fieldreceiver 34 of the interrogator means 12.

FIG. 3 illustrates one embodiment of a squaring amplifier 60 useful inthe practice of the invention herein and, in particular, the embodimentof the responder tag 22 shown in FIG. 2. As shown, the squaringamplifier 60 receives the frequency f, signal from coil 46 throughresistor 80 and capacitor 82 and is applied therefrom to the base 86 ofa transistor 84. The emitter 88 of transistor 84 is connected to the 28VDC bus and the base to emitter connection is provided through diode 90.The collector 92 of the transistor 84 is connected to ground throughresistor 94 and the squared frequency f signal is obtained at thecollector electrode 92 of transistor 84 for application to the counter68 and filter 62.

The gated linear amplifier 64 shown in FIG. 2 may also be comprised of aparticular circuit that has been found useful in the practice of thepresent invention in the responder tag 22. FIG. 4 illustrates a circuitdiagram for one embodiment of a gated linear amplifier 64 that has suchutility. As shown on FIG. 4 the gated linear amplifier 64 is comprisedof the amplifier 98 which, for example, may be an RCA CA3002 thatreceives the frequency f signal from the filter 62 at a first terminal106 thereof. A second terminal 102 is connected to ground throughresistor 104. Resistor 106 also provides a ground connection for thefrequency f signal applied to first terminal 100. The +6 volt signalfrom the diode bridge 48 is applied to third terminal 108 of theamplifier 98 and the 6 volt signal from the diode bridge 50 is appliedto fourth and fifth terminals 110 and 112. The frequency f data signalfrom the multiplexer 66 is applied to sixth terminal 114 of theamplifier 98 and is biased to the 6 volt signal through resistor 116. Atthe output terminal 118 of the amplifier 98 there is provided thefrequency f signal modulated by the frequency f, data signal which isapplied to the coil 76 for transmission back to the interrogator 12.

In the above description of the responder tag 22, it will be appreciatedthat one particular embodiment of the invention has been illustrated anddescribed. Many variations of the particular circuit details may be madeby those skilled in the art. For example, the three filter rectifierdiode bridges 48, 50 and 52 could be replaced with just one filterrectifier diode bridge to provide a single output voltage of, forexample, +12 VDC which would then be utilized for all tag operations.Similarly, in other variations of the present invention, the filterrectifier diode bridges could be replaced by a full wave rectifier. Itwill be appreciated, of course, that in preferred embodiments of thepresent invention it is desired to have a high degree of flux capture bythe coil such as coils 42, 44 and 46. Therefore, in such preferredembodiments of the invention it is desired to utilize high permeabilitycoils to achieve the highest degree of flux capture within a given tagdimension.

ln other variations of the present invention, squaring amplifier 60 maybe replaced by a self-contained oscillator operating at frequency f orat any other frequency substantially less than frequency f,; and/orfilter 62 may be replaced by a self-contained oscillator operating atfrequency f and/or gated linear amplifier 64 may be replaced by theappropriate functions required to achieve other forms of modulation suchas frequency modulation or phase modulation; and/or filter 62 and gatedlinear ampiifier 64 may be replaced by a gated oscillator which is gatedby the data signal from counter/multiplexer 66 and which is controlledin frequency by the series combination of coil 76 and capacitor 77;and/or counter/multiplexer 66 may be replaced by any of the commonlyknown forms of generating serial information signals such as parallelinput-serial output shift registers, johnson counters, and the like. Asnoted above the present invention also contemplates utilization of apreferred form of interrogator structure arrangement wherein the powerfield is inductively coupled to the responder tag and the codedinformation field is received from the responder tag to provideappropriate reading and identification of the information contentcontained herein.

FIG. illustrates a portion of the interrogator 12 partially in blockdiagram form and partially in schematic diagram form. As shown on FIG. 5there is provided a power supply means 14 utilized to generate thevarious voltage signals necessary for operation of the interrogator 12.The power supply 14 receives conventional 115 V, 60 cycle power at aninput indicated at 120. This input power is applied to a transformer 122at the primary 124 thereof. The secondary 126 of the transformer 122 isa center tap to ground at 128 and the secondary 126 is connected to a +5VDC regulator 130 and a VDC fused metered regulator 132. A pilot light134 is connected across the secondary 126 of transformer 122 for avisual observation of the operational condition thereof. The +5 VDCregulator 130 provides a +5 VDC signal at the output 136 thereof that,as noted below, is utilized in various portions of the structure.Similarly, the +30 VDC regulator 132 provides +30 VDC signal at itsoutput 138 for utilization in a +12 VDC regulator 141) and otherportionsof the interrogator 12 as described below. The +12 VDC regulatorprovides, as an output thereof, a +12 VDC signal at a first output 142,a +12 VDC display signal 144 that is utilized only for the high orderand low order display as indicated below and a +l 5 VDC signal at athird output 146. The +15 VDC signal and +12 VDC signal are utilized inother structure of the interrogator 12 as described below. Thus, in thisembodiment of the present invention there is provided the +5 VDC signal,the +30 VDC signal, the +15 VDC signal, the +12 VDC signal and the +12VDC display signal which are utilized for the various operationsrequired in the interrogator 12. Other structural adaptations andarrangements of the interrogator 12 may utilize the same or othersignals. It will be appreciated that the power supply 14 may be readilyadapted by those skilled in the art to provide the voltages and/orsignal contents necessary for utilization in any desired type ofinterrogator according to the principals of the present invention.

The time-base generator 16 shown on FIG. 5 incorporates the frequency foscillator 150, for example f, =50 kilol-lertz as mentioned above, thatis powered by the +12 VDC signal. The signal from the frequency foscillator is fed into a clock generator 152 that is powered by the +12VDC signal and the +5 VDC signal and provides, at its output 154 thereofthe squarewave frequency 2X f clock signal (which is double thefrequency of the signal from the frequency f oscillator 150.) Thefrequency 2X f clock signal is utilized as the time clock basethroughout the operation of the interrogator 12 in the applications andportions thereof as described below. Phase adjustment on the clockgenerator 152 may be provided by, for example, variable resistor 156connected thereacross.

As noted above the interrogator 12 provides, as part of its function,the generation of a power signal which is coupled to an electromagneticpower field generator for subsequent inductive coupling to the respondertag. The power signal generator 18, as shown on FIG. 5, is generallycomprised of a frequency f chopper 160 that receives the frequency foscillator output signal at a first input'terminal 162 thereof and apower switching signal at a second input terminal 164 thereof. Thegeneration of the power switching signal is described below inconnection with FIG. 7. Thus, the frequency f chopper provides an outputsignal at the output terminal 166 thereof that is chopped as indicatedby the waveform shown. This chopped frequency f signal is fed into apower amplifier 168, that is powered by the +30 VDC signal from thepower supply 14 and the output signal from power amplifier 168 at theoutput terminal 170 thereof is the power signal that is transformed toan electromagnetic power field to be inductively coupled from theinterrogator 12 to the responder tag 22.

As noted above, the coupling of the power field to the responder tag 22is preferably by inductive coupling between the interrogator 12 and theresponder tag 22 and, as such, the interrogator 12 is provided withthree field generation coils 172, 174 and 176. For convenience, on FIG.5, these coils are merely shown in conventional circuit diagram format.However, in practice, in this embodiment of the present invention, thecoils are generally arranged in mutually orthogonal fashion in the X, Yand Z axis. FIG. 6 illustrates such an arrangement of the coilspreferred for operation of the interrogator 12. Thus, first coil 172 maybe oriented in the plane of the X Z axis. Second coil 174 may beoriented in the plane of the Y Z axis and third coil 176 may be orientedin the X Y axis. These coils 172, 174 and 176 may, in some embodimentsof the present invention, be made comparatively large and be placedcompletely surrounding, for example, a moving belt upon which theluggage or cargo or other item having a responder tag 22 thereon ismoving. As such an item moves through the field generated by the threemutually perpendicular coils 172, 174 and 176 power is applied to thecoil for activation of the responder tag 22 which, in response to thepower field received, generates and inductively couples back to theinterrogator 12 the coded information field. In the present embodimentof the invention the three coils 172, 174 and 176 function as both thepower field generator as well as the coded information field receiver34. That is, not only do the three coils 172, 174 and 176 generate thepower field for the power field receiver 24 of the responder tag 22 butalso receive back the coded information field from the coded informationfield generator 32 of the responder tag 22. In this embodiment of thepresent invention this combined field generation and receivingcapability is conducted substantially simultaneously by the three coils172, 174 and 176 as controlled by control signals from the decodestages, as described below, applied to a pair of relay drivers coupledto relays associated with each coil. Thus, first coil 172 is controlledby operation of a first sense relay 178 and a first power relay 180. Thefirst sense relay 178 is controlled by a first sense relay driver 182that receives an appropriate control signal from the decode stages.Similarly, the first power relay 180 is controlled by a first powerrelay driver 184 that also receives a control signal from the decodestages. Thus, the first coil 172 may generate a power field uponselective operation of the power relay 180 from the signal received fromthe power amplifier 168 applied to the input 186 of the first coil 172.The first power relay 180 receives its power from the +15 VDC signalgenerated in the 12 VDC regulator 140 of the power supply means 14.Similarly, the first coil 172 may be utilized to receive the codedinformation field from the coded information field generator 32 of theresponder tag 22 by selective operation of the first sense relay 178 bythe first sense relay driver 182. The first sense relay 178 receives the+12 VDC power from the 12 VDC regulator 140 of the power supply stage 14and when selective operation of the first sense relay 178 and firstpower relay 180 by the appropriate control signals applied to theirrespective relay drivers is achieved the coded information field may becoupled from the responder tag 22 back to the interrogator 12. Theoutput 188 of the first coil 172 is connected to a capacitor 190 that isconnected to ground potential.

Similarly, the second coil 174 has an input 192 and an output 194. Theoutput 194 is connected to a second capacitor 196 that is also connectedto ground potential. Signals are applied to the input 192 of the secondcoil 174 by selective operation of a second power relay 198 and a secondsense relay 200. The second power relay 198 also receives its power fromthe +15 VDC signal and the second sense relay 200 receives power fromthe +12 VDC signal. The second power relay 198 is controlled by secondpower relay driver 202 and the second sense relay 200 is controlled bysecond sense relay drive 204. Both the second sense relay drive 204 andthe second power relay driver 202 receive their controlling signals fromthe decode stages as described below.

The third coil 176 also has an input 206 and an output 208. The output208 is connected to a capacitor 210 that is connected to groundpotential. Power is supplied to the third coil 176 in the mannerdescribed above for the first coil 172 and second coil 174. The thirdcoil 176 receives its power from the signal generated in the poweramplifier 168 applied to the input 206 upon selective operation of thethird power relay 212 receiving its power from the +15 VDC signalgenerated in the +12 VDC regulator of the power supply 14. A third senserelay 214 powered by the +12 volt signal from the +12 VDC regulator 140of the power supply 14 is selectively operated to allow receipt of thecoded information field from the coded information field generator 32 ofthe responder tag 22. The third sense relay 214 is controlled by a thirdsense relay driver 216 and the third power relay 212 is controlled bythe third power relay driver 218, both of which receive their controlsignals from the decode stages as indicated below.

In the preferred embodiment of the present invention, as noted above,the three coils 172, 174 and 176 are sequentially operated in thegenerate and receive signal conditions by selective operation of thefirst power relay 180, second power relay 198, third power relay 212 andthe first sense relay 178, second sense relay 200 and third sense relay214. One mode of such sequential operation that has been found to beadvantageous in the practice of the present invention has been to haveone coil in the generate condition, that is generating a power field forthe responder tag 22 by applying the power amplifier 168 output signalto the coil. For example, coil 172 as shown in FIG. 5 is in the powerfield generation condition for the positions of the first power relayand first sense relay 178.

During the time that power is being applied to the coil 172 forinductive coupling to the responder tag 22 the second coil 174 and thethird coil 176 are sequentially operated in the receive mode through thesecond sense relay 200 and third sense relay 214. That is, in this modeof operation the second coil 174 may be in the receive condition thatis, with the relay 198 not energized and in the opposite position fromthat shown in FIG. 5 and the second sense relay 200 energized into theopposite position shown in FIG. 5. This allows transmission of thesignal from the coil 174 into the interrogator 12, as described below.During this time period that the second coil 174 is in the receivingposition the third coil 176 is in a null condition. That is, the thirdpower relay 212 would be in the opposite position from that shown inFIG. 5 and the third sense relay 214 would be deenergized and in theposition shown in FIG. 5 and thus no field would be either generated orreceived by the third coil 176. This receive condition by the secondcoil 174 and simultaneous null condition by the third coil 176 continuesfor one-half of the time period that the first coil 172 is in thegenerate condition and then the second coil 174 is switched to the nullcondition and the third coil 176 is switched to the receive condition.This simultaneous operational condition continues for the second half of17 the generate time period for the first coil 172. After thissequential operation involving the first coil 172, second coil 174 andthird coil 176, the second coil 174 may be switched to the generatecondition and the first coil 172 and third coil 1'76 sequentially in thereceive and null conditions. Then the third coil 176 may be in thegenerate condition and the first coil 172 and second coil 174sequentially operated in the null and receive condition. It will beappreciated that other selective sequential operating modes of the threemutually perpendicular coils 172, 174, and 176 may be selected forswitching between the generate receive and/or null conditions. Specificapplications may require specific cycling and sequencing operations.

In the preferred embodiments of the present invention, in order tominimize power utilization, it is preferred that the power fieldgenerated by the coils 172, 174 and 176 be pulsed. While pulsing may notbe necessary in applications where unlimited power is available at thepower input 120 to the power supply 14, in other and perhaps more remotelocations where battery power or other types of limited power isavailable to the interrogator 12 the pulsing arrangement of power intothe coils is desirable to minimize the electrical energy utilized. Thecurrent associated with the 30 VDC signal is preferably monitored inorder to detect if the coils 172, 174 and 176 which are in the presentapplication of .the invention tuned for air generation and receiving,become detuned due to presence of a large metal or iron objects nearthem. Such objects would change the inductance of the coils and therebydetune them from resonance at frequency f for which they are air tunedand thus decrease the generated power field. In order to maintain thepower field at a given magnitude regardless of adjacent metal objectsthe power amplifier 168 may incorporate a current regulation capabilityso that a constant power is applied to the coils regardless of thepresence (or absence) of adjacent metal or other detuning structure.Altemately, in order to maintain the power field at a given magnituderegardless of adjacent metal objects the frequencyf oscillator may beregulated to provide a frequency output which tracks the resonantfrequency of the coils.

It will be appreciated that, in order to minimize arcing when relays areutilized to control the three coils 172, 174, 176, it is preferred thatthe switching of the relays take place when no power is applied thereto.It will also be appreciated that the relay utilization may be replacedby appropriate solid state devices such as silicon controlled rectifiersand the like.

Thus, at any given instant of time at least one of the three coils 172,174, 176 are in the signal receiving condition of operation. As such,when a coded information field is being generated by a responder tag 22it is received and fed to a frequency f notched filter 220, as shown onFIG. 5, which is part of the coded information signal detector 36. Thenotched filter is utilized to filter any components of the interrogatorpower field which might be cross coupled from the particular coil of thethree coils 1'72, 174, 176 which are in the generate condition to thecoil that is in the signal receiving operational condition. It will beappreciated by those skilled in the art that even through the coils 172,174, 176 are preferably orthogonal, there may be 18 some amount of crosscoupling between the generating and receiving coils due to the toleranceon the degree of orthogonality provided and because of some fielddistortion resulting from the presence of the responder the particularresponder tag 22 present within the field of the three coils 172, 174and 176. Alternately, in

order to eliminate the cross coupling at frequency f,, a

high pass filter may be utilized as a replacement for notched filter220.

The signal from the output 224 of the frequency f notch filter 220 isapplied to an amplifier-demodulator 226 that is powered by the +12 VDCsignal. The amplifier-demodulator 226 provides the function of bothamplification of the above-mentioned amplitude modulated signal anddemodulation of the resultant amplified signal in order to recover theresponder data signal. The amplifier-demodulator is, as with othercomponents of the system of the present invention,

preferably a semiconductor device and as such may be I a NationalSemiconductor, Inc. Model LN372 amplifier-demodulator. The demodulatedsignal from the output 228 of the amplifier-demodulator 226 is appliedto the input terminal 230 of an amplifier stage 232 that is powered by a+5 VDC signal. The amplifier provides a second stage of amplificationfor the demodulated signal and it has been found that in the presentinvention an RCA Model CA 3002 amplifier may be utilized. The amplifiedsignal from the output 234 of the amplifier 232 is applied to an inputterminal 236 of a logic buffer 238 that is powered by the +5 VDC signal.The logic buffer provides a demodulated data in the form of voltage andcurrent levels that are compatible with the particular circuitryutilized in the logic section 38 described below. It has been found thata transistor driving a TTL logic element may be utilized to provide theappropriate voltage and current levels necessary for the particular typeof circuitry utilized in the logic stage 38. The data signal at theoutput terminal 240 of the logic bufier 238 is the data signalcorresponding to the particular tag 22 presented in appropriate digitalform for utilization by the logic section 38.

FIG. 7 illustrates the logic section 38 of the interrogator 12 accordingto one embodiment of the present invention. As shown, a data gate 240receives the digital data signal from the logic buffer 238 at the inputterminal 244 thereof. The data gate 242 provides a gated data signal atan output terminal 246 thereof which is applied to the input terminal248 of a data flip flop 251). The data flip flop 250 also receives aclock pulse signal (CP). A divider 252 receives the frequency 2Xf1 clocksignal from clock generator 152 and divides it into two oppositelyphased clock signals CP 1 and CP 2. The two oppositely phased clocksignals CP 1 and CP 2 are fed into a clock phase select 254 whichalternately feeds one or the other of the clock signals CP 1 or CF 2 toa 15 stage counter 256, and to other structure of the logic section 38described below. The 15 stage counter 256 has stages a, b, c, d, e, f,g, h, j, x, y, k, l, m and n. The clock signal, whether CP 1 or CF 2 isfed into stage a of 15 stage counter 256 and the 15 stage counter 256 isa digital counter and counts the clock pulses, whether CP 1 or CP 2digitally. When the counter is full that is all for example digital 1'sup to stage j of 15 stage counter 256 a signal is sent from stage j backto clock phase select 254 and the clock phase select then switches from,for example, CP 1 to CP 2. Thus the signal received from stage jcontinuously switches from one to the other of the two oppositely phasedsignals CP 1 and CP 2 which is then provided at the output terminal 254of the clock phase select 254.

In this embodiment of the present invention the lower frequency stagesof the digital counter 256, such as stages x, y, k, l, m and n, areutilized for providing the appropriate signals for control of the relaydrivers associated with each of the three coils 172, 174 and 176 shownon FIG. 5. Thus, a power relay decode means 260 receives signals fromstages m and n of the 15 stage counter and upon receipt of such signalsappropriately generates, sequentially, the control signals for the powerrelay drivers 182, 204 and 216 (shown in FIG. 5) that control theoperation of the power relays 180, 198 and 212 respectively for enablingeach of the three coils 172, 174 and 176 to be sequentially in the powerfield generation condition. A power on decode stage 262 receives signalsfrom the k and l stages of the stage digital counter 256 and, inresponse thereto, generates the appropriate control signal for providingthe pulsed signal for the frequency f chopper 160. A sense relay decodemeans 264 is provided and receives signals from the y, k, l, m and nstages of the 15 stage digital counter 256 and, in response thereto,generates the control signals for control of the sense relay drivers182, 204 and 216 for control of the sense relays 178, 2111) and 214,respectively, of the coils 172, 174 and 176 respectively, to allow thecoils to be sequentially switched into the receiving or the nullcondition.

The x, k and 1 stages of the 15 stage counter 256 also are utilized toprovide an enabling signal for the information validation portion of thelogic means 38. Signals from the x, k and l stages of the 15 stagedigital counter 256 are applied to the data gate 242. The data gate 242operates to transmit the data signal from the logic buffer 238 to thedata flip flop 250 when the appropriate x, k and lsignals are present.FIG. 8 illustrates some of the characteristic signals of the logicsection 38 during this time period when the appropriate at, k and lsignals are present. For purposes of example only, it may be assumedthat the responder tag 22 is designed to provide a repetitive 16 bitdata word. Thus, 16 separate bits of information may be encoded in theresponder tag 22 and such 16 bits will include both the informationcontent desired in the responder tag 22 as well as any preselectedsynchronizing sequence.

During the time period when the appropriate 1:, k and l signals arepresent, there are 32 transmissions of the 16 bit data word. Since thesetransmissions can begin with any particular data bit in the total 16 bitword of the responder tag 22, there being no particular clock or timingrelationship in this embodiment of the invention between the responderand interrogator, the validation and capture logic network is required.On FIG. 7 the validation and capture logic section 39 of the logic 38provides these functions of validating and capturing the signal. Ingeneral, the validation and capture process may be considered as one inwhich there is a comparison of the transmissions received during the 0 1signal and the 0 2 signal. If the transmissions are identical, the shiftclock is stopped and the data is thereby captured for display, audiosignal, visual signal or whatever desired capture indicating techniquemay be desired in any individual application. If the transmissionsduring the 0 1 and the 0 2 signal periods are not identical, thecomparison process is repeated during the next sequential 0 l and 0 2signal periods. It will be appreciated that other checks on validtransmission can be performed. Such techniques as parity, errordetection and/or correction codes, or a greater number of successiveidentical transmissions required to establish validation are well knownto those practiced in the art. The particular type of validation andcapture utilized in any particular application may be that determined byother system parameters.

During the O 1 signal period the O 1 signal is applied to therecirculation control gates 261 from the phase decode stage 263. Thephase decode stage 263 receives an input signal at a first inputterminal 265 from the f stage of the 15 stage counter 256 and a secondinput signal at a second input terminal 266 from the e stage of the 15stage counter 256. Thus there is provided a 0 1 signal at a first outputterminal 268 of the phase decode stage 263 and a 0 2 signal at a secondoutput terminal 270 of the phase decode stage 263. The data signal fromthe data flip flop is also applied to the recirculation control gates ata data signal input terminal 272. During O 1 signal time periods thecomparison control gates 274 are disabled and the non-compare flip flop276 is held at reset. During the 0 1 signal period a 16 bit transmissionis gated through the recirculation control gates from the outputterminal 278 thereof to the input terminal 280 of a 16 bit serial dataregister 282.

During the 0 2 signal period, the data which had previously been putinto the 16 bit serial data register 282 is allowed to recirculate inthe 16 bit serial data register 282 through the recirculation controlgate 261 by application of the signal therefrom at an output terminal284 back to an input terminal 286 on the recirculation control gates261. The 0 1 signal is applied to the recirculation control gates 261 ata third input terminal 288.

During the 0 2 signal time period the comparison control gates 270,which also receive the information from the 16 bit serial data register282 at an input terminal 290 as well as the 2 signal at a second inputterminal 292 and the data signal from the data flip flop 250 at a thirdinput terminal 294 providing an output signal at an output terminal 296,are enabled to permit the bit by bit comparison of the data from theserial register at output terminal 284 thereof with the data from thedata flip flop 250. Thus, there is achieved a comparison of twosuccessive transmissions. If the two transmissions during the O 1 signaland 0 2 do not compare, the process is repeated during next and all sub21 sequent cycles beginning with the 1 signal time period until acomparison is obtained. FIG. 8 shows the possible conditions for datatransmission at the data line where a V equals valid and an I equalsinvalid, and the resultant effect on the state of the non-compare flipflop on the nc line. If the two successive transmissions do not resultin a comparison during the 0 2 signal period then the non-compare flipflop 276 remains reset and a capture of the data in the field coupledfrom the responder 22 through the data flip flop 250 is achieved duringthe period of time from the end of 0 2 to the beginning of the next 0 1.That is, when the signal at stage f of the 15 stage counter 256 is alogic or a digital 1. During this time period, when a comparison exists,the data in the 16 bit serial data register 282 is recirculating. When asynchronization character which may be utilized in the signal as notedabove is detected in bit positions 2 through 9 by the synchronizationcharacter detect gate 300 a signal is sent from an output terminal 302thereof to an input terminal 304 on a stop shift control gate 306. Thisenables the stop shift control gate and since the stop shift controlgate also receives an output signal from an output terminal 297 of anon-compare flip flop 276 at an input terminal 308 thereof as well as abit signal from the f stage of the 15 4 stage counter 256 at a thirdinput terminal 310, the stop shift flip flop 312 is set by the signalfrom the output terminal 314 of the stop shift control gate applied tothe input terminal 316 of the stop shift flip flop. When the stop shiftflip flop 312 is set an output signal at an output terminal 318 thereofis sent to a tone oscillator 320 having a volume adjust reostat 322 andwhich is powered by a +12 VDC signal for, if desired, an audio signalfrom the speaker 324. At the same time the output signal from the outputterminal 318 of the stop shift flip flop 312 is sent to the stop shiftdelay flip flop 326 which sets the stop shift delay flip flop 326 uponreceipt of the next clock pulse (CP). Setting the stop shift delay flipflop 326 disables the shift clock gate 328 by the signal applied at aninput terminal 330 thereof from the output terminal 332 of the stopshift delay flip flop 326. Disabling the shift clock gate 328 preventsthe application of the signal from the output terminal 334 thereof frombeing applied to the 16 bit serial data register 282. Since there is aone clock time delay from the synchronization character detection to theserial data register stop, such a one clock time delay allows thesynchronization character and data to assume their proper position inthe appropriate bit positions of the 16 bit serial data register 282.The data in bit positions nine through 16 is then held, due to thesetting of the stop shift delay flip flop 326 for static display, or anyother type of display or communication desired. 2

It will be appreciated by those skilled in the art that the entirevalidation and capture logic portion 39 of logic 38 may be adjusted toaccommodate any desired number of data bits that can be encoded into theresponder tag 22. It is only necessary to provide sufficient capacity insuch components as, for example, the sixteen bit serial data register282 or the 15 stage I counter 256. In certain applications it may bedesired to provide a SYSTEMS CLEAR signal which removes the display ofthe information data content in the detected signal and prepares theinterrogator to receive information fields from subsequent respondertags. In such applications the system clear (SC) signal is applied tothe 16 bit serial data register 282, non-compare flip flop 276, stopshift flip flop 312 and the stop shift delay flip flop 326.

In this embodiment of the invention the clock pulse (CP) is shifted 180from the CP 1 to the CP 2 when the 15 stage digital counter 256 has anappropriate change of signal at stage j thereof. Thus, during the firsthalf of the time period that the appropriate 1:, k and l signals arepresent, data is clocked into the data flip flop 250, which alsoreceives the clock pulse from the clock phase select 254, with CP 1 andduring the second half of the appropriate x, k and I signal time periodthe data is clocked in at GE 2. Such an arrangement has been found to benecessary where the phase relationship and polarity of the received datasignal is unknown with respect to the interrogator timing system. Itwill be appreciated that if appropriate timing synchronization or selfclocking communication techniques are incor- I porated this particulararrangement need not be utilized. This concludes the description of apreferred embodiment of the present invention. From the above it will beappreciated that there has been described a complete interrogatorresponder system wherein a passive responder tag may be utilized with anappropriate interrogator to detect the particular digital code containedin the responder tag. While the above embodiment describes theutilization of the present invention in a three dimensional detectionmode, it will be appreciated that a substantially flat plane type ofinterrogator may be utilized in which only two power field generationcoils are utilized wherein the power field is projected toward theresponder tag instead of requiring the responder tag to be physicallypassing through the coil arrangement. Such an embodiment providesacceptable two dimensional detection capability and, due to the fluxinterchange, approximately 15 to 20 of three dimensional detectioncapability also. Thus such a unit would be designed to be situated alongside of the appropriate responder tag or structure housing the respondertag. In a portable configuration the unit would be appropriately movedaround to detect the presence of the responder tag. Thus manually threedimensions can be covered with the two coil two dimensional arrangement.FIGS. 9 and 10 illustrate one such embodiment of an interrogator,generally designated 400 useful for a primarily two dimensional signaltransmission and signal detection application. As shown in FIGS. 9 and10, the arrangement 400 may be considered a portable handheld unit whichis provided with a handle 402 for appropriate carrying and positioning.An electronic section 404 houses the appropriate electronics similar tothatdescribed above for the interrogator 12 except that, for example, inthis embodiment there may be a self-contained source of electricalenergy such as a battery (not shown) within the electronic section 404.Alternately, the electronics section 404 may be housed in a separatelycarried or mounted structure. A coil section 408 is provided and houseswithin it a pair of orthogonal power generation coils and a receivingcoil. The arrangement of the coils is shown in FIG. 10. One of the coils410 is wound in a manner to have the long portions of the coil parallelto the top surface 412 and bottom surface 414 of the coil

1. An interrogator-responder system for providing an output signalhaving an information content corresponding to an uniquely codedinformation field of a particular responder, and generated in saidresponder, in response to the interrogator, and comprising, incombination: an interrogator means for establishing an electromagneticAC power field and receiving an electromagnetic coded information field,and generating the output signal in response thereto; a responder tagmeans positionable in AC power field and coded information field energyexchange relationship to said interrogator means for receiving said ACpower field and generating the uniquely coded information field inresponse thereto; said interrogator means comprising: a power supplymeans for providing a controlled source of electric energy; a powersignal generator means for receiving said controlled electric energy andgenerating a power signal in response thereto; a power field generatormeans for receiving said power signal and generating said AC power fieldhaving a first preselected frequency for inductive coupling into saidresponder tag means; a coded information field receiver means forreceiving said uniquely coded information field from said responder tagmeans and said uniquely coded information field having a secondpreselected frequency different from said first preselected frequency;coded information field detection means powered by said controlledsource of electric energy, for detecting the existance of said codedinformation field in said coded information field receiver means andgenerating a detected coded signal in response thereto; informationcapture and validation logic means, powered by said controlled electricenergy, for receiving said detected coded signal from said codedinformation field detection means and generating an output signal havingan information content corresponding to said uniquely coded informationfield in response thereto; time-base signal generating means forgenerating a time-base signal and providing said time-base signal tosaid power signal generator and to said logic means for synchronization;said responder tag means is free of active power supplies and comprises:power field receiver means for receiving said AC power field from saidpower field generator of said interrogator means and providing DC tagpower signals in response thereto; carrier time-base signal generatormeans for receiving said DC tag power signal and generating a carriertime-base signal at said second preselected frequency in responsethereto; a code signal generator powered by said DC tag power signal forrepetitively generating a unique code signal at a third frequencydifferent from said second frequency in response to said DC tag powerinput thereto; coded information signal generator means powered by saidDC tag power signal for receiving said carrier time-base signal at saidsecond frequency and receiving said unique code signal at said thirdfrequency and modulating said carrier time-base signal with said uniquecode signal to generate a coded information signal unique to saidresponder tag; coded information field generator for receiving saidcoded information signal and generating said coded information field forsaid inductive coupling into said coded information field recEiver ofsaid interrogator means.
 2. The arrangement defined in claim 1 whereinsaid code signal generator further comprises: binary signal generatingmeans for generating an unique digital binary code signal having aplurality of information bits and a first portion of said plurality ofinformation bits comprises a common binary bit sequence forsynchronizing said coded information signal, and a second portion ofsaid plurality of information bits comprises an unique binary bitsequence; said logic means of said interrogator means further comprises:sequence detection means for detecting said common binary bit sequencein said detected coded signal of said coded information signal detectorand generating said output signal in response to said unique binary bitsequence in said coded information field.
 3. The arrangement defined inclaim 2 wherein said interrogator is inductively coupled to saidresponder tag means for providing said AC power field to said respondertag means and receiving said coded information field from said respondertag means, and said power field generator and said coded informationfield receiver of said interrogator means together comprise: a pluralityof interrogator coils oriented in a preselected geometric array and eachof said coils is sequentially operable in a plurality of conditions, afirst of said conditions comprising a field generating condition forgenerating said AC power field and a second of said conditionscomprising a coded information field receiving condition for receivingsaid coded information field (1) from said responder tag means; saidinterrogator means further comprising: switching means coupled to saidplurality of interrogator coils for sequentially switching each of saidplurality of interrogator coils from each of said plurality ofconditions to another of said plurality of conditions at a predeterminedswitching frequency and in a preselected sequential order; said codedinformation signal generator of said responder tag means furthercomprises: a responder tag coil means; said power field receiver of saidresponder tag means further comprises: a coil means for inductivelycoupling said AC power field into said responder tag; DC voltagemagnitude limiting means for limiting the magnitude of said DC tag powersignals generated by said power field receiver means in response to saidAC power input field.
 4. The arrangement defined in claim 3 wherein:said plurality of interrogator coils comprises three coils and saidpreselected geometric array comprises a orthogonal array of said coils,and said switching means further comprises means for at least switchingeach of said coils from said first condition to said second conditionand from said second condition to said first condition in apredetermined order to provide two of said three coils simultaneously insaid first condition and one coil in said second condition whereby saidinterrogator detects said coded information signal for said respondertag in any geometric orientation with respect to said interrogator coilsof said interrogator means.
 5. The arrangement defined in claim 4wherein: said responder tag is positionable in regions adjacent theintersection of the axis of said mutually orthogonal interrogator coils.6. The arrangement defined in claim 5 wherein: said first preselectedfrequency and said third preselected frequency are each on the order of50 kiloHertz, and said second preselected frequency is on the order of450 kiloHertz.
 7. The arrangement defined in claim 4 wherein: said codedinformation signal generating means of said responder tag means furthercomprises: means for amplitude modulating said carrier time-base signalwith said code signal.
 8. The arrangement defined in claim 4 wherein:said coded information signal generating means of said responder tagmeans further comprises: means for phase modulaTing said carriertime-base signal with said code signal.
 9. The arrangement defined inclaim 4 wherein: said coded information signal generating means of saidresponder tag means further comprises: means for frequency modulatingsaid carrier time-base signal with said code signal.
 10. The arrangementdefined in claim 2 wherein: said interrogator means is inductivelycoupled to said responder tag means for providing said AC power inputfield to said responder tag means and for receiving said codedinformation field from said responder tag means; said power fieldgenerator of said interrogator means comprises: a pair of elongatedinterrogator coils, each of said pair of elongated interrogator coilshaving a long axis and a short axis and geometrically arranged to havesaid long axis perpendicular to each other for simultaneously generatingsaid AC power field; said coded information field receiver of saidinterrogator means comprises: a receiving coil positioned in closeproximity to said pair of interrogator coils; said coded informationfield generator of said responder tag means further comprises: aresponder tag coil means; said power field receiver of said respondertag means further comprises: a coil means for inductively coupling saidpower field into said responder tag; DC voltage limiting means forlimiting the magnitude of said DC tag power signal generated by saidloop-stick means in response to said AC power field.
 11. The arrangementdefined in claim 10 wherein: said interrogator coils and said receivercoil are enclosed in a field transmitting case means.
 12. Thearrangement defined in claim 11 wherein: said first preselectedfrequency and said third preselected frequency are on the order of 50kiloHertz and said second preselected frequency is on the order of 450kiloHertz.
 13. The arrangement defined in claim 10 wherein: said codedinformation signal generating means of said responder tag means furthercomprises: means for amplitude modulating said carrier time-base signalwith said code signal.
 14. The arrangement defined in claim 10 wherein:said coded information signal generating means of said responder tagmeans further comprises: means for phase modulating said carriertime-base signal with said code signal.
 15. The arrangement defined inclaim 10 wherein: said coded information signal generating means of saidresponder tag means further comprises: means for frequency modulatingsaid carrier time-base signal with said code signal.
 16. The arrangementdefined in claim 2 wherein: said power field generator means and saidcoded information field receiver means together comprise a plurality ofthree mutually orthogonal coils for inductive coupling between saidresponder tag and said interrogator means, and said mutually orthogonalcoils are sequentially operated in a power transmit condition, a signalreceiving condition and a null condition in a preselected sequence. 17.The arrangement defined in claim 2 wherein: said power field generatormeans and said coded information field receiver means comprise: a pairof mutually orthogonal coils, a first of said pair of coils comprisingsaid power field generator means; and a second of said pair of coilscomprises a coded information field receiver for receiving a codedinformation field from said responder tag.
 18. The arrangement definedin claim 2 wherein: said interrogator means further comprises means forpulsing said power field provided to said responder tag.
 19. Thearrangement defined in claim 2 and further comprising: clock generatormeans for generating a clock signal having a predetermined frequencysubstantially twice the frequency of said AC power field provided tosaid responder tag.
 20. The arrangement defined in claim 19 wherein:said coded information sIgnal detection means further comprises: a notchfilter for receiving said coded information signal from said codedinformation field receiver means and filtering said coded informationsignal to remove components of interrogator power cross coupled thereinfrom said power signal transmitter; an amplifier-demodulator stage forreceiving the output from said notch filter means for amplifying thesignal received from the notch filter and demodulating said amplifiedsignal; an amplifier means for further amplifying saidamplified-demodulated signal; and a logic buffer means for receiving theamplified-modulated signal and converting same to said detected codedsignal having a predetermined voltage and a predetermined current. 21.The arrangement defined in claim 20 wherein: said logic means furthercomprises a validation and capture portion for validating the trueinformation content of said detected coded signal applied thereto fromsaid coded information signal detection means and providing displaythereof on a preselected display means for the condition of saidinformation signal validated.
 22. The arrangement defined in claim 21wherein: said logic means further comprises: a digital counter having apredetermined plurality of stages, a first portion of said stages forgenerating control signals, and a second portion of said stages forgenerating opposite phased signals, and said opposite phased signalsapplied to said validation and capture portion; said control signals forproviding sequencing control to said power signal transmitter means andsaid coded information signal receiver means for sequencing in apredetermined sequence, and for pulsing said power signal generator toprovide a pulsed power field to said responder tag.
 23. A passiveresponder tag means comprising, in combination: a power field receivermeans for receiving an AC power field inductively coupled thereto andproviding DC tag power signals in response thereto; carrier time-basesignal generating means for receiving said DC tag power signal andgenerating an AC carrier time-base signal at a first predeterminedfrequency in response thereto; a code signal generator powered by saidDC tag power signal for repetitively generating an unique code signal ata second frequency different from said first frequency in response tosaid DC tag power signal input thereto; coded information signalgenerating means powered by said DC tag power signal for receiving saidcarrier time-base signal at said first frequency and for receiving saidunique code signal at said second frequency and for modulating saidcarrier time-base signal with said unique code signal to generate acoded information signal unique to said tag responder; coded informationfield generating means for receiving said coded information signal andgenerating an electromagnetic coded information field in regionsexternal of said responder tag means.
 24. The arrangement defined inclaim 23 wherein: said code signal generator means further comprisesbinary signal generating means for generating an unique binary codesignal having a plurality of information bits and a first portion ofsaid plurality of information bits comprises a common binary bitsequence for keying said coded information signal, and a second portionof said plurality of binary information bits comprises an unique binarybit sequence; said coded information field generator means furthercomprises: a responder tag coil means; said power field receiver meansfurther comprises: a coil means for inductively coupling said AC powerfield into said responder tag means; and DC voltage limiting means forlimiting the magnitude of said DC tag power signals.
 25. The arrangementdefined in claim 24 wherein: said coil means comprises four diode bridgemeans for converting said AC power input signal to said DC tag powersignals and said DC volTage limiting means comprises a zener diode. 26.The arrangement defined in claim 25 wherein: said coded informationsignal generating means further comprises amplitude modulation means foramplitude modulating said carrier time-base signal with said codesignal.
 27. The arrangement defined in claim 24 wherein: said codedinformation signal generating means further comprises phase modulationmeans for phase modulating said carrier time-base signal with said codesignal.
 28. The arrangement defined in claim 24 wherein: said codedinformation signal generating means further comprises frequencymodulation means for frequency modulating said carrier time-base signalwith said code signal.
 29. The arrangement defined in claim 24 wherein:said binary signal generating means further comprises a binary codegenerator, and said common binary bit sequence in said binary codesignal is represented by an eight bit binary notation P1111110; and saidfirst preselected frequency of said carrier time-base signal is on theorder of 450 kiloHertz and said second preselected frequency of saidcode signal is on the order of 50 kiloHertz.
 30. The arrangement definedin claim 25 wherein: said binary code generator comprises a metal oxidemultiplexor.
 31. The arrangement defined in claim 25 wherein: saidbinary code generator comprises a complimentary metal oxide multiplexor.32. The arrangement defined in claim 25 wherein: said binary codegenerator comprises a silicon on sapphire multiplexor.
 33. Aninterrogator-responder system for providing an output signal having aninformation content corresponding to an uniquely coded information fieldindicative of a particular responder and generated therein in responseto the interrogator and comprising, in combination: an interrogatormeans for establishing an electromagnetic AC power field and receivingan electromagnetic coded information field, and generating the outputsignal in response thereto; a responder tag means positioned in AC powerfield and coded information field energy exchange relationship to saidinterrogator means; said responder tag means is free of active powersupplies and comprises: power field receiver means for receiving said ACpower field from said interrogator means and providing DC tag powersignals in response thereto; carrier time-base signal generator meansfor receiving said DC tag power signal and generating a carriertime-base signal at a second preselected frequency in response thereto;a code signal generator powered by said DC tag power signal forrepetitively generating a unique code signal at a third frequency inresponse to said DC tag power input thereto; coded information signalgenerator means powered by said DC tag power signal for receiving saidcarrier time-base signal at said second frequency and receiving saidunique code signal at said third frequency and modulating said carriertime-base signal with said unique code signal to generate a codedinformation signal unique to said responder tag; coded information fieldgenerator for receiving said coded information signal and generatingsaid coded information field for said inductive coupling into said codedinformation field receiver of said interrogator means.
 34. Aninterrogator-responder system for providing an output signal having aninformation content corresponding to an uniquely coded information fieldindicative of a particular responder and generator therein in responseto the interrogator and comprising, in combination: an interrogatormeans for establishing an AC electromagnetic power field and receivingan electromagnetic coded information field, and generating the outputsignal in response thereto; a responder tag means positionable in powerfield and coded information field energy exchange relationship to saidinterrogator means for receiving saiD AC power field and generating saiduniquely coded information field in response thereto; said interrogatormeans comprising: a power supply means for providing a controlled sourceof electric energy; a power signal generator means for receiving saidcontrolled electric energy and generating a power signal in responsethereto; a power field generator means for receiving said power signaland generating said AC power field having a first preselected frequencyfor inductive coupling into said responder tag means; a codedinformation field receiver means for receiving the uniquely codedinformation field from said responder tag means and the uniquely codedinformation field having a second preselected frequency different fromsaid first preselected frequency; coded information detection meanspowered by said controlled source of electric energy for detecting theexistence of said coded information field in said coded informationfield receiver means and generating a detected coded signal in responsethereto; information capture and logic means, powered by said controlledelectric energy, for receiving said detected coded signal from saidcoded information field detection means and generating an output signalhaving an information content corresponding to said uniquely codedinformation field in response thereto; and time base signal generatingmeans for generating a time base signal and providing said time basesignal to said power signal generator and to said logic means forsynchronization.
 35. An interrogator means for establishing an ACelectromagnetic power field and receiving and identifying anelectromagnetic coded information field transmitter thereto, andgenerating an output signal in response to said identifiedelectromagnetic coded information field, and comprising: a power supplymeans for providing a controlled source of electric energy; a powersignal generator means for receiving said controlled electric energy andgenerating a power signal in response thereto; a power generator meansfor receiving said power signal and generating the AC power field havinga first preselected frequency for transmitting said AC power field toregions remote the interrogator; a coded information field receivermeans for receiving a coded information field from regions esternal tothe interrogator and said coded information field having a secondpreselected frequency different from said first preselected frequency;coded information field detection means powered by said controlledsource of electric energy for detecting the existence of said codedinformation field in said coded information field receiver means andgenerating a detected coded signal in response thereto; informationcapture and validation logic means powered by said controlled source ofelectric energy for receiving said detected coded signal from said codedinformation field detection means and generating an output signal havingan information content corresponding to said uniquely coded informationfield in response thereto; and time base signal generating means forgenerating time base signal and providing said time base signal to saidpower signal generator and to said information capture and validationlogic means for synchronization.
 36. The arrangement defined in claim 35wherein said power field generator and said coded information fieldreceiver together comprise: a plurality of interrogator coils orientedin a preselected geometric array and each of said coils is sequentiallyoperable in a plurality of conditions, a first of said conditionscomprising a power field generating condition for generating said powerfield and transmitting said power field to regions remote theinterrogator and the second of said conditions comprising a codedinformation field receiving condition for receiving said uniquely codedinformation field from regions external the interrogator; and saidinterrogator means further compriSing: switching means coupled to saidplurality of interrogator coils for sequentially switching each of saidplurality of interrogator coils from each of said plurality ofconditions to another of said plurality of conditions at a predeterminedswitching frequency and in a preselected sequential order.
 37. Thearrangement defined in claim 36 wherein: said plurality of interrogatorcoils comprises three coils and said preselected geometric arraycomprises an orthogonal array of said coils, and said switching meansfurther comprises means for at least switching each of said coils fromsaid first condition to said second condition and from said secondcondition to said first condition in a predetermined order to providetwo of said three coils simultaneously in said first condition and onecoil in said second condition whereby said interrogator detects saidcoded information signal for said responder tag in any geometricorientation with respect to said interrogator coils of said interrogatormeans.
 38. The arrangement defined in claim 36 wherein: said firstpreselected frequency is on the order of 50 kH and said secondpreselected frequency is on the order of 450 kH.
 39. The arrangementdefined in claim 36 wherein said validation and logic means of saidinterrogator further comprises: sequence detection means for detecting aunique binary bit sequence in the detected coded signal of said codedinformation signal detector and generating said output signal inresponse to said unique binary bit sequence in said coded informationfield.
 40. The arrangement defined in claim 36 wherein: said power fieldgenerator of said interrogator means comprises: a pair of elongatedinterrogator coils, each of said pair of elongated interrogator coilshaving a long axis and a short axis and geometrically arranged to havesaid long axis perpendicular to each other for simultaneously generatingsaid AC power field; said coded information field receiver of saidinterrogator means comprises: a receiver coil positioned in closeproximity to said pair of interrogator coils.